The process for recovery of copper metal values from ores and processing liquids by solvent extraction-electrowinning (hereafter, "SX-EW") is well-known. Briefly, the process is carded out using a copper-bearing aqueous solution which is obtained by dissolving (generally from an ore) the copper in an aqueous leach liquor, or by using a copper-bearing solution such as process effluent. The resulting solution of copper values is mixed with a water-immiscible organic solvent (e.g., kerosene) containing a water-insoluble ion exchange composition having selective affinity for the copper values. The ion exchange composition preferentially extracts the copper values from the aqueous solution. The aqueous and organic phases are separated. The aqueous solution, now copper-depleted, is usually referred to as "raffinate." The raffinate can be recycled as leach liquor (in a leaching process) or discarded (in a process such as recovery of copper from process effluent). The organic phase (which contains ion exchange composition and the extracted copper values) is usually referred to as "loaded organic." The desired copper values are removed from the loaded organic by mixing with an aqueous strip solution containing strong acid such as sulfuric, phosphoric, or perchloric acid, and having lower pH than the above copper-bearing aqueous solution. The aqueous strip solution extracts the desired copper values from the loaded organic. After separation of the organic and aqueous phases, the desired copper values are present in the aqueous strip solution. The resulting copper-rich aqueous strip solution is usually referred to as an "electrolyte" or "rich electrolyte." The copper-depleted organic phase is usually referred to as a "barren organic." The barren organic can be recycled.
Copper is recovered in purified form from the electrolyte by a technique known as "electrowinning" (hereafter sometimes referred to as "EW"). The electrowinning process typically involves plating the copper on copper starting sheets or stainless steel cathode mother blanks. The plating cycle usually takes about seven days to obtain a 100-pound cathode from each side of the mother blank. The cathodes are stripped mechanically from each side of the mother blank and are then available for further processing which can include drawing, rolling, etc. Often these cathodes are transported to a rod plant wherein they are subjected to continuous casting. After recovery of the desired copper, the copper-depleted electrolyte, which is sometimes referred to as "lean electrolyte," can be recycled as aqueous strip solution for fresh loading with copper values.
The production of copper powder by electrodeposition involves the use of an electrolytic cell containing an anode, a cathode, an electrolyte solution containing copper ions and sulfate ions, and a source of current. Through the application of voltage between the anode and the cathode the deposition of copper powder is effected on the cathode surface. The powder is then removed at timed intervals or in a continuous fashion. The process begins with the copper feed stock which is dissolved in sulfuric acid to form the electrolyte solution. Relatively pure electrolytes are required so that the copper powder is of sufficient purity for normal commercial purposes such as friction materials, beatings, alloying additives, powder metallurgy, etc. Copper removed from the electrolyte by the electrolytic production of copper powder is typically continuously replenished in order to maintain the concentration of the copper ions in solution. The purity of the electrolyte and the replacement of copper removed from the electrolyte is maintained by the use of relatively pure copper soluble anodes. The copper used for the anodes has been previously purified by electrolytic means to remove undesired contaminants. The electrolytically purified copper is typically recast into an anode shape suitable for powder production. An alternative method involves the use of electrolytically purified copper rods approximately 1/2-inch in diameter cut into 1-inch lengths and called copper shot which are then placed in an insoluble wire mesh anode basket..
The production of copper foil by electrodeposition also involves the use of an electroforming cell containing an anode, a cathode, an electrolyte solution containing copper ions and sulfate ions, and a source of current. Through the application of voltage between the anode and the cathode the deposition of copper is effected on the cathode surface. The copper feed stock, which is dissolved in sulfuric acid to form the electrolyte solution, is an electrolytically purified form of copper such as copper shot, copper wire, copper oxide or recycled copper. The resulting copper sulfate solution is then purified in order to ensure that high purity copper sulfate required for the production of foil is generated. Various types of agents for controlling the properties of the foil such as animal glue and thiourea can be added to the electrolyte solution. The electrolyte solution is pumped into the electroforming cell, and with the application of voltage between the anode and cathode, the electrodeposition of copper takes place. Typically the process involves using cylindrical cathodes that may be of varying diameters and widths. The anodes conform to the curvature of the cathodes so as to maintain a constant separation or gap between the two.
The electrolytically purified copper feedstocks used in prior art electrodeposition processes for making copper powder and copper foil are often produced using SX-EW techniques of the type discussed above. They are also made using traditional smelting and refining techniques. The prior art electrodeposition processes, which involve initially dissolving the copper feedstock in a digester to form copper ions, are slow, difficult to control, and require large quantities of expensive pure copper inventoried in the digester. It would be advantageous if copper powder could be produced directly from relatively impure sources of copper such as copper ore or copper-containing waste without the additional steps of first recovering copper using electrolysis and then dissolving the pure copper metal to obtain copper ions for the electrolyte solution. It would also be advantageous if copper foil could be produced from a source of copper that was relatively pure and readily digestible in sulfuric acid. The present invention provides such advantages.
By virtue of the inventive process copper powder is produced in a simplified and less costly manner when compared to the prior art. The inventive process utilizes a copper source that does not require in its production the additional steps of electrowinning, drawing, etc., which are used in making the electrolytically purified copper feedstocks (e.g., copper shot, copper wire, copper oxide, recycled copper, etc.) used in the prior art. Impurities carried from the extraction steps used in the inventive process to the electrolyte solution used to make the copper powder do not degrade the performance characteristics of the copper powder. The copper powder made by the inventive process can be dissolved in sulfuric acid to form electrolyte solutions. These electrolyte solutions can be used to make copper foil and thus the foil-making process provided for herein is more easily controlled and more efficient than the prior art methods for making such foil. The copper powder can also be calcined to form cuprous oxide, cupric oxide or a mixture thereof. These copper oxides can be readily dissolved in sulfuric acid and used to make copper foil.
The article by I. D. Enchev et al, "Production of Copper Powder by the Method of Electrolytic Extraction Using a Reversing Current", Poroshkovaya Metallurgiya, No.9 (141), September, 1974, pp. 95-98, discloses the results of an investigation into the production of copper from electrolytes prepared from lean ore solutions by ion exchange or reversing electrolytic extraction. Electrolyte solutions prepared by leaching ore wastes and subsequent extraction with ABF dissolved in kerosene were used. The article indicates that the disclosed process yields a high-purity powder (99.98% copper) at an oxygen content of 0.2-0.4 %.